In a paper published in 1905 attention was drawn to the increase that had taken place in the consumption of animal food in this country in the past fifty years. It was there pointed out that the amount of meat imported into this country had increased from 3 lbs. per head per annum in 1853 to 50 lbs. per head per annum in 1903 - a very remarkable increase. A consideration of these figures suggests the question, What amount of animal protein is requisite for the healthy nutrition of normal subjects? The results of Chittenden's recent researches on the amount of protein requirements in health have clearly shown that in some important respects the teaching of the text-books on diet is erroneous and have shown the necessity of, in the words of a leading writer, reconsidering our conclusions on diet from their foundations. The necessity for such a reinvestigation has further been demonstrated by the results of some preliminary observations on diet, investigated from a new standpoint, published by me in 1904-5, which showed that the administration of an excessive meat diet to normal animals was followed by striking histological changes in the thyroid gland. This evidence of structural change in the thyroid gland under a meat diet indicated the advisability of repeating the experiments on a larger scale. I have during the past year made an extensive series of observations on the influence of a meat diet on (a) the growth and general nutrition, and (6) the structure and functions of the organs of a large number of animals. The present paper deals with the former; it gives an account of the clinical results obtained by feeding rats on an exclusive flesh diet and also some comments on the bearing of these results on some clinical phenomena in the human subject. The diets employed were ox-flesh and horse-flesh, With bread and milk as the control diet. The chemical composition of these dietaries was determined by Dr Andrew Hunter, assistant in the physiological laboratory of the University of Edinburgh, and is elsewhere given in detail.1 The essential facts are summarised in the following table: -
1 Chalmers Watson, Lancet, vol. ii., 1906.
Bread and milk..
Bread and milk is the diet in common use for tame rats, and the control diet used in this experiment was found to be admirably adapted for the growth and nutrition of rats of all ages. In connection with the experimental diets it may be mentioned that under certain conditions - e.g. in the neighbourhood of abattoirs - the diet of wild rats is mainly one of flesh food of different kinds. .Some control observations were made on the influence of the two dietaries (horse-flesh and bread and milk) on wild rats. The effects of the diet were studied in animals of different ages as follows: (1) on very young rats newly weaned (three weeks old), the controls being taken from the same litter - twenty-five rats with nineteen controls; (2) on young rats, approximately two and a half months old - twenty-two rats with twelve controls; and (3) on full-grown adult rats - fourteen rats with ten controls. In the investigations special attention was directed to the following points: (a) the effects of the diet on the growth and nutrition of the meat-fed animals; (b) the health of their offspring; and (c) the recuperative power of a norma! diet in animals which had deteriorated as a result of the meat-feeding.
Fourteen young rats from five litters, newly weaned, were placed on an exclusively ox-flesh diet, eleven rats from the same litters being used as controls (bread and skimmed milk diet). Five of the meat-fed animals succumbed within four months, their weights and date of death being indicated on Chart 1. The remaining nine animals lived and appeared to thrive, but they gained in weight less than did the controls. Two representative illustrations are given. These show the relative sizes of two male rats of the same litter after being fed for three months on bread and skimmed milk (Fig. 8a) and ox-flesh (Fig. 8b) respectively. The general appearance of these nine ox-flesh-fed subjects was in all respects normal; it was, however, observed that some of them moved about in a less lively manner than did normal animals. This lessened activity was associated with, and apparently dependent upon, changes in the osseous system of a rachitic-like nature which were revealed at the post-mortem examination. In the meat-fed animals flitters four and five) four were females, and although kept with males none of them became pregnant, whereas of the three control females from the same litters all bore litters. These results admit of the following conclusions: - 1. Very young rats, newly weaned, can in the majority of cases live and thrive on an exclusive ox-flesh diet; their growth is, however, retarded by this dietary. 2. An ox-flesh diet interferes with the development of pregnancy.
1 Journal of Physiology, vol. xxxiv., No. 112.
Fig. 8. - To show the relative size of two male rats of the same litter after being fed for three months on bread and skimmed milk (a) and ox-flesh (b).
Fig. 9. - To show the state of development of the progeny of normally fed (bread and milk) rats (a) in comparison with rats of the same age bred on a flesh diet (b).
[Face page 666.